Sunset for Dawn

NASA's Dawn mission has come to an end; the spacecraft has run out of propellant, and is no longer able to point its antenna at Earth. I've seen numerous posts online from distraught astronomers and space enthusiasts - this post will add to that cacophony.

The Dawn spacecraft visited the two most massive bodies in the main asteroid belt: asteroid 4 Vesta, and dwarf planet Ceres; Dawn orbited both of these bodies - a first in spaceflight history.

Dawn was propelled by an ion drive; with barely a breath of thrust, its engine operated for tens of thousands of hours; Dawn set the record for velocity change produced by a spacecraft's engines.

I've followed the Dawn mission since its launch; "The Dawn Mission at Asteroid Vesta" was the first topic I lectured about as a volunteer NASA/JPL Solar System Ambassador. So much new and interesting information kept pouring in during the mission, I had to update my Dawn lecture continuously; I've written about Dawn extensively on this blog.

For the past several days, I've had the NASA/JPL Deep Space Network Now website up on one of my screens - I saw when Dawn stopped communicating on the days mentioned in the NASA/JPL press release below; I knew it was coming, but my heart still sank.

However, there has been some controversy concerning Vesta's status as a protoplanet. In an article posted on Icarus in April of 2015, Br. Guy Consolmagno and several other authors ask "Is Vesta an intact and pristine protoplanet?" This article has been referenced in several places - in it, the authors suggest that Vesta either formed from source material with non-chondritic composition, or after its formation underwenta radical physical alteration, possibly caused by collisional processes, that affected its global composition and interior structure.

The authors argue that data from the Dawn mission support that Vesta is not an "intact protoplanet," but possibly reaccreated after a catastrophic collision. I'm not sure how widely this hypothesis is accepted throughout the ranks of planetary scientists, but I notice that the word "protoplanet" does not appear in the NASA/JPL press release below.

Related to this topic: Br. Guy and I had an interesting email conversation in 2014 about "2nd generation differentiation in a re-accreated body" - he got to talking about aluminum in the crustal material, re-melting, and that there are questions about Vesta that need to be followed-up upon. Br. Guy mentioned "So far, I am still just trying to get the rest of the field to recognize that those are interesting questions."

The Dawn spacecraft will remain in an elliptical orbit around dwarf planet Ceres for several decades to come.

Following NASA’s strict planetary protection protocols, my engineers have placed me in an orbit around Ceres that should remain stable for decades. I’ll continue to circle as a satellite around one of the worlds I studied for so long.That’s no moon. That’s me. pic.twitter.com/rFzkzI8Cq9

This photo of Ceres and the bright regions in Occator Crater was one of the last views NASA's Dawn spacecraft transmitted before it depleted its remaining hydrazine and completed its mission. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA's Dawn spacecraft has gone silent, ending a historic mission that studied time capsules from the solar system's earliest chapter.

Dawn missed scheduled communications sessions with NASA's Deep Space Network on Wednesday, Oct. 31, and Thursday, Nov. 1. After the flight team eliminated other possible causes for the missed communications, mission managers concluded that the spacecraft finally ran out of hydrazine, the fuel that enables the spacecraft to control its pointing. Dawn can no longer keep its antennae trained on Earth to communicate with mission control or turn its solar panels to the Sun to recharge.

Video: Dusk for Dawn: NASA Mission to the Asteroid Belt:

The Dawn spacecraft launched 11 years ago to visit the two largest objects in the main asteroid belt. Currently, it's in orbit around the dwarf planet Ceres, where it will remain for decades.

"Today, we celebrate the end of our Dawn mission - its incredible technical achievements, the vital science it gave us, and the entire team who enabled the spacecraft to make these discoveries," said Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate in Washington. "The astounding images and data that Dawn collected from Vesta and Ceres are critical to understanding the history and evolution of our solar system."

Animation of Dawn's trajectory around 4 Vesta from 15 July 2011 to 10 September 2012. CC BY-SA 4.0

Dawn launched in 2007 on a journey that put about 4.3 billion miles (6.9 billion kilometers) on its odometer. Propelled by ion engines, the spacecraft achieved many firsts along the way. In 2011, when Dawn arrived at Vesta, the second largest world in the main asteroid belt, the spacecraft became the first to orbit a body in the region between Mars and Jupiter. In 2015, when Dawn went into orbit around Ceres, a dwarf planet that is also the largest world in the asteroid belt, the mission became the first to visit a dwarf planet and go into orbit around two destinations beyond Earth.

"The fact that my car's license plate frame proclaims, 'My other vehicle is in the main asteroid belt,' shows how much pride I take in Dawn," said Mission Director and Chief Engineer Marc Rayman at NASA's Jet Propulsion Laboratory. "The demands we put on Dawn were tremendous, but it met the challenge every time. It's hard to say goodbye to this amazing spaceship, but it's time."

The data Dawn beamed back to Earth from its four science experiments enabled scientists to compare two planet-like worlds that evolved very differently. Among its accomplishments, Dawn showed how important location was to the way objects in the early solar system formed and evolved. Dawn also reinforced the idea that dwarf planets could have hosted oceans over a significant part of their history - and potentially still do.

Asteroid 4 Vesta. Image credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA

"In many ways, Dawn's legacy is just beginning," said Principal Investigator Carol Raymond at JPL. "Dawn's data sets will be deeply mined by scientists working on how planets grow and differentiate, and when and where life could have formed in our solar system. Ceres and Vesta are important to the study of distant planetary systems, too, as they provide a glimpse of the conditions that may exist around young stars."

Because Ceres has conditions of interest to scientists who study chemistry that leads to the development of life, NASA follows strict planetary protection protocols for the disposal of the Dawn spacecraft. Dawn will remain in orbit for at least 20 years, and engineers have more than 99 percent confidence the orbit will last for at least 50 years.

So, while the mission plan doesn't provide the closure of a final, fiery plunge - the way NASA's Cassini spacecraft ended last year, for example - at least this is certain: Dawn spent every last drop of hydrazine making science observations of Ceres and radioing them back so we could learn more about the solar system we call home.

The Dawn mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. JPL is responsible for overall Dawn mission science. Northrop Grumman in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team.

A Mercator projection and has a resolution of 460 feet (140 meters) per pixel. The images used to make this map were taken from Dawn's high-altitude mapping orbit (HAMO), at a distance of 915 miles (1,470 kilometers) from Ceres. Source: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

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Bob is a lifelong amateur astronomer, and former outreach officer for the Warren Astronomical Society, and a volunteer NASA/JPL Solar System Ambassador. Bob does a lot of astronomy outreach - he lectures about astronomy and space science, and sets up his telescopes at schools, planetariums, conventions, and other venues. From 2014-2016, he was the editor of the Warren Astronomical Society's newsletter.

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